Normally a so-called fluorescence standard is used for calibrating a measured intensity value of the fluorescent light, which standard emits fluorescent light of a known wave length distribution and intensity when irradiated with excitation light of a preset wave length and intensity. However the long-term stability of this kind of fluorescence standards is usually insufficient. A method and an apparatus for the determination of the fluorescence of a test sample are for instance known from the document EP 0 237 363 A2.
It is therefore the object of the invention to provide a method which guarantees a reliable and repeatable calibration of the measured fluorescent light also over longer periods of time.